If it was rejected for AGI—-be aware that many 2020 returns took so long for the IRS to process that your 2020 AGI might not be in the IRS system. Try using zero instead.
If filing with zero is rejected then file again but select the option that you did not file last year. The IRS does not see that question and it will allow you to e-file with no AGI question.
https://ttlc.intuit.com/community/agi/help/where-do-i-correct-my-agi-in-turbotax-online/00/26311
If that does not work and you still cannot e-file, then print, sign, and mail your tax return.